This invention relates to specialized valves and valve systems for use in fluid systems. More specifically, it relates to liquid marking systems wherein ink is applied in droplets or as a stream of material to various surfaces for marking purposes. Such systems are often referred to as drop on demand or ink jet marking or printing systems. In one example of such systems, ink is pressurized and forced through a nozzle to create tiny drops which may be controlled electrostatically or otherwise to determine where and when they will strike the article to be marked. In another example a drop is created on demand and directed toward the article to be marked.
For brevity throughout the specification such systems, regardless of type, will be referred to as liquid or ink marking systems. Such equipment is used for many applications including, but not limited to, industrial marking applications as, for example, date coding on food and beverage packing lines, addressing magazine labels, and the like.
The ink used in ink jet marking equipment possesses a particular range of properties, among which are included viscosity, conductivity, density, etc., which must be maintained within specified limits to insure proper operation. Because the ink may be recycled many times from the nozzle back to the ink supply, over a period of time, this could be a reason for change of physical characteristics to occur. One of the primary causes of this change is the evaporation of the solvent portion of the ink. Thus, as the ink is sprayed from the nozzle and the unused portion thereof returned by the catcher to the ink supply, solvent evaporates to the atmosphere adversely affecting the ink's properties. It is necessary to provide means to replace this solvent loss to obtain reduced equipment maintenance and extended service from the ink supply.
Automatic solvent re-supply systems are known in the art. Generally they consist of a detector associated with the ink supply reservoir which signals when solvent should be added and a means for transporting the solvent from a container to the ink supply reservoir. The detector portion of these systems, forming no part of the present invention, can be of various types. Some detectors weigh the ink supply and add solvent when a certain weight loss is detected. Others measure the volume or the specific gravity of the ink. The present invention, which is a valve suitable for controlling the flow of any fluid including solvent may be used with any suitable detector as detailed hereafter.
As indicated, the invention is suitable for use in connection with solvent transport in a liquid marking system. It can, however, be utilized in many other applications with equal success. For example, the valving system of the invention can also be used to gate the flow of ink in a system, such as disclosed in U.S. Pat. No. 4,121,222 assigned to the present assignee. Indeed, the valve can be used in any application where it is desired to transfer a liquid from one location to another.
A current method for transporting liquids in ink jet marking systems involves the use of a small, electrically energized pump for the purpose of liquid transport. That system requires a separate component and the attendant expense and utilization of additional space. Apart from the added initial costs, there may be more maintenance costs. Another example for transporting liquid from one location to another in a marking system involves use of an air operated valve. Such a system is disclosed in U.S. Pat. No. 3,930,258. Such valves, while operating satisfactorily, can be improved with respect to reliability, system compatibility, size and, in particular, cost. Such components are relatively large and quite expensive.
The present invention seeks to overcome the disadvantages of existing liquid transport valves and permit the design of a controlled liquid flow system which uses more simply operable and lower cost valves. More specifically, the present invention permits valving of solvent using means which are small and low cost and which permit a manufacturer of marking fluids, such as solvent and inks, to insure the integrity of the chemicals used.